Several network types exist for delivering media content, such as video, data, voice, or high-speed Internet services to subscribers. In a cable television (CATV) network, for example, the network may take the form of an all-coax, all-fiber, or hybrid fiber/coax (HFC) network, delivering media content from a headend to subscriber client devices. In addition to transporting data traffic, as well as television content signals over a CATV network, multiple services operators (MSO) also use their network infrastructure for carrying voice, video on demand (VoD) and video conferencing traffic signals, among other types.
Radio Frequency (RF) over Glass (RFoG) is a fiber to the premise (FTTP) technology that may operate concurrently with an HFC network, such as out of the same headend/hub in a cable network. Premise may include a home, business, or other location. RFoG permits the continued use of traditional HFC equipment and back-office applications with fiber-to-the-premise deployments. For example, RFoG enables cable operators to reuse existing headend equipment and infrastructure of Data Over Cable Service Interface Specification (DOCSIS) service delivery. Thus, use of existing cable modem termination system (CMTS) platforms, headend equipment, set-top boxes, and cable modems can continue while gaining benefits inherent with RFoG systems. For example, concurrent RFoG/HFC operation enables the use of RFoG for node splitting, which may increase capacity in an existing HFC network.
Communications downstream (or forward) may be straightforward in that the downstream communications are sent to all receivers, but only the intended receivers decode or utilize the data. However, communication in the upstream (or return) direction may be prone to interference. For example, a phenomenon called optical beat interference (OBI) may occur in RFoG systems when the signals from two return transmitters hit a receiver simultaneously on the same wavelength, or when the wavelength separation is small (e.g., <200 pm). In a cable system, for example, the condition that causes OBI can easily occur in multiple-dwelling unit (MDU) applications of DOCSIS-based systems with bonded upstream channels. OBI can potentially impact the entire return path performance and will become an increasing concern as return path bandwidth and utilization grows.
Methods to prevent the interference have been proposed, such as scheduler-based and physical layer (PHY)-based solutions. The scheduler-based and physical layer (PHY)-based solutions organize the upstream transmissions in a way that only one of the offending upstream devices sends data at one time to any particular optical receiver. In the physical-layer solution, even if two offending upstream devices can send data at the same time (as would be the case with bonded D3.0 channels), other precautions are taken such that no two upstream devices emit optical signals at precisely the same optical wavelengths. Using the scheduler-based approach, upstream and downstream solutions for communicating data may be provided without experiencing interference.